Wireless identification systems and protocols

ABSTRACT

Monitoring systems and protocols are disclosed that are flexible in mode operation and format depending on the environment in which they are used. Such monitoring systems and protocols are able to change their utilization automatically, or by received instruction to do so. A location detection system includes one or more low frequency transmitters, one or more radio frequency monitoring tags and one or more receiving devices. The low frequency transmitter transmits location identification information, such as the transmitter ID, to a tag in the vicinity of the transmission. The tag relays the transmitter ID using a higher frequency transmission sent from the tag to the receiver. Communication protocols are disclosed that enable deciphering of multiple tag transmissions starting simultaneously.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of and claims priority toU.S. patent application Ser. No. 10/172,713 filed Jun. 14, 2002 byLastinger et al., which claims priority to U.S. Provisional PatentApplication Ser. No. 60/298,322, filed Jun. 14, 2001, the respectivedisclosures of which are incorporated herein by reference.

BACKGROUND

1. Field of the Invention

The present invention relates to wireless identification systems andprotocols and more specifically to systems used for detection,identification, control and/or location of events and/or objects.

2. Related Art

Conventional data communication systems have been applied to accomplishobject identification using the medium of radio broadcast. Such radiofrequency identification (RFID) systems find application in the fieldsof materials handling, inventory control, and generally in the field oftracking personnel, objects, and animals.

Wireless monitoring systems, such as tag systems, are well known fordetecting, locating and/or identifying coded articles. A variety oftechniques and systems have been used to determine the identificationand/or location of a suitably tagged article. Two basic approaches existfor these tag systems:

The first approach is the use of tags that intermittently orrepetitively beacon or broadcast identification, status, or other sensorinformation without necessarily requiring interaction from otherdevices. When thousands of beacon type tags are present in a confinedenvironment the intermittent broadcasts often overlap or collide anddifficulty is encountered in distinguishing reception of overlapping orcolliding broadcasts from multiple tags. In an attempt to overcome thisproblem, it is known to vary the periods between tag broadcasts, varythe length and type of tag transmissions and other types of variationsto provide broadcast diversity in multiple tag environments. This typeof intentional variation in tag broadcast is referred to asnon-synchronous or Type I transmissions.

A second approach is to use tags that are able to receive transmissionsfrom other devices or sense the occurrence of an event. In thisapproach, the tags receiving transmissions from other devices mayrespond to such transmissions by broadcasting information. This approachis analogous to an interrogate and respond system where when informationis desired from the tag, a transmission is sent to the tag requestingthat it respond with, for example, identification, location, sensorinformation. When a request for information transmission is broadcast,for example by a reader unit or interrogator, the tags in the area ofbroadcast respond by transmitting the requested information in their ownbroadcast. This second type of transmission is referred to as asynchronous or Type II transmission.

These systems are designed for the detection of a single type of event,such as the detection of a merchandise tag entering a designated areaand are directed to a particular application having predeterminedsurveillance area (e.g., adjacent to and exit or loading/unloadingpoint). Conventionally, these systems are typically designed and presetfor specific applications and thus different tags and equipment arerequired for various differences purpose (e.g., beacon type tags versesresponding or interrogation type tags). These specific designs representfixed configurations of systems for utilization with particularapplications.

In other applications multiple receivers are positioned at selectedpoints in a surveillance area, for example distributed throughout awarehouse. The receivers are able to identify a location of a tag by forexample, the time of receipt, angle of arrival, signal strength and/orphase difference of the transmissions from the transmitting tag or tags.

Conventionally, these systems are confined to single purposeapplications. Different tags, readers, protocols and software arerequired for different system applications. The foregoing systems tendto be relatively complex and expensive because: (i) the number ofreceivers deployed for surveying an area increases costs of suchsystems; and (ii) the predefined function of a tag or system requiresspecific equipment and inventories for each type of application, whichalso increases associated costs.

Accordingly, it would be beneficial to have monitoring systems andprotocols that are flexible depending on the environment in which theyare used, wherein such systems and protocols are able to change theirutilization automatically, or by programmed instruction to do so.

Moreover, it would be advantageous to have a location detection systemwhere the numbers of complex receiving devices can be reduced.

It would further be advantageous to have monitoring systems that areconfigured so that tag collisions (i.e., simultaneous receipt of tagtransmissions) can be reduced or deciphered and validated moreeffectively.

BRIEF DESCRIPTION OF THE DRAWING

Additional aspects, features and advantages of the present inventionwill become more apparent from the following description of the appendeddrawing in which like reference numerals denote like elements and inwhich:

FIGS. 1A and 1B are plan views of an exemplary monitoring systemaccording to various aspects of the present invention;

FIG. 2 is a plan view of the FIG. 1A monitoring system in use with aloading device and containers;

FIG. 3 is a functional block diagram of a tag according to variousaspects of the present invention;

FIG. 4 is a functional block diagram of a signal strength analyzeraccording to various aspects of the present invention;

FIG. 5 is a functional block diagram of the system of FIG. 1A inimplementation;

FIG. 6 is a flow diagram of a method of monitoring according to variousaspects of the present invention;

FIG. 7 is a functional block diagram illustrating a location monitoringsystem including a navigational receiver;

FIG. 8 is a timing diagram of a protocol for communicating according tovarious aspects of the present invention; and

FIG. 9 is a message word format including subparts.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Location Monitoring Systems

Systems according to various aspects of the present invention track thelocation and movement of objects, animals or personnel for maintaininginventory status, providing access to portions of a facility (e.g.,unlocking doors for a particular personnel), directing materialshandling equipment, and assisting in discovering the location ofobjects, animals and personnel.

For example, a system according to various embodiments of the inventionincludes a transmitter or locator unit to broadcast information within alocalized area. This type of transmitter is referred to herein as a“locator” or “locator unit.” The following terms are also assigned thefollowing meanings: “area” is defined to mean a physical position or afacility (e.g., a yard, building, floor, suite, bay, or unit of storagespace); “locator ID” is an identification of a locator that isbroadcasting; “zone” is an area of signal reception that may be definedby a strength and direction of signal broadcast as well as a sensitivityof a particular receiver; “tag ID” is an identifying piece ofinformation that uniquely defines a tag or tag finction; “Beacon rate”is the reciprocal of the sum of duration of transmitting a message andthe time between message transmissions; “synchronous” means Type IItransmissions that are synchronized at the receiver end according to aquery/response protocol; “asynchronous” or “non-synchronous” means TypeI transmissions which have no regard to a receiving device or otherbroadcast signal; a “tag message” is a broadcast from a tag.

A monitoring system according to various aspects of the presentinvention may be used to track identification and position of, forexample, inventory, order movement, and/or shipments of articles eachhaving monitoring tags attached thereto. By way of example, a warehouseor other facility housing a large number of articles may have aplurality of fixed low frequency transmitters or “locators” positionedat various locations around the warehouse, each transmitter having aspecified zone of transmission. A grid or matrix of such fixed locatorsmay be arranged to have overlapping zones of transmission to increasethe accuracy of locating of tagged items. When each locator broadcastslocation information (e.g. Locator ID, geographical coordinates), anytags in the respective zone of transmission respond by broadcastingtheir own transmissions. Such tag broadcasts include the locationidentification information received from the one or more locators thatinitiated the tag broadcast. A receiving device or monitor may receivethe tag broadcasts and associated processing equipment may determine alocation of the responding tags using the location identificationinformation. By overlapping zones of transmissions, the tags may belocated with greater accuracy (e.g., between the overlapping area of twoor more zones).

Locators may also be positioned at various doorways, access points,processing devices (e.g., loaders or assembly line points) or otherareas of interest to enable the monitoring system to detect when the tag(and associated article) reaches such an area of interest. In this case,the locator zones of transmission may not overlap with other locatorssince it may only be desired to know when a tag enters into the zone oftransmission of a specific locator.

Turning to FIG. 1A, a monitoring system 100 may include one or morelocators 110, 120, one or more tags 130, and one or more monitors 140.

Locators 110, 120 serve the function of broadcasting transmissions,including location information, in an area to be monitored. Tags 130serve the purpose of receiving information broadcast from locators 110,120 and broadcasting their own transmissions including the locationidentification information received from locators 110, 120. Monitors 140serve the purpose of receiving broadcasts from tags 130 or othertransmit devices such as locators 110, 120. Monitor 140 may alsofunction to process received information and/or provide receivedinformation to one or more processing units 150 over a wireless or wirednetwork 160.

Each locator 110, 120 has a zone 111, 121 for which it is set tobroadcast and a unique Locator ID associated therewith. If a tag (e.g.,tag 130) is present in zone 111 or zone 121 the tag receives the locatorbroadcast (including Locator ID) from each respective locator. Each tagreceiving a locator broadcast then broadcasts its own message, includingthe Locator ID, Tag ID and any other sensor and control information suchas battery status, time of day, etc. (collectively, message 133).Monitor 140 receives and decodes the tag broadcast and passes thedecoded information through network 160 to processor 150. Processor 150then tracks the identification and determines the location of tag 130based on the Locator ID and Tag ID.

If tag 130 falls in an area of overlap of two or more zones, e.g., zone111 and zone 121 (as shown), one or more messages 133 may include bothLocator IDs for respective locators 110 and 120. In this manner,processor 150 can locate tag 130 with increase accuracy because of thelimited area of overlap between zone one and zone two.

Message 133 may include one or more of the following pieces ofinformation:

-   -   Tag ID;    -   Locator ID, IDs and/or other geographical information such as        GPS coordinates;    -   SSI (signal strength indicator) of received locator signal (may        include more than SSI if receiving more than one locator        signal); and    -   Time of Day or other pertinent information such as battery        level, last transmission, control codes, etc.

Locators 110 and 120 may be any device or combination of devices forperforming the functions of broadcasting location information (e.g.,Locator ID, positional coordinates) in a predefined area or zone. In apreferred embodiment, because of their relatively close proximity totags, locators 110 and 120 emit relatively low power and relatively lowfrequency transmissions. Locators 110 and 120 may also use extremelydirectional antennas that limit the range of respective transmissions toprevent significant overlapping of locator transmissions. The additionof more locators and overlapping zones of transmission can be used toincrease the accuracy of location determination.

Referring to FIG. 1B, system 100B includes four locators each havingrespective broadcast zones. System 100B also includes an additional asecond monitor 142 serving to monitor a different area, e.g., AREA 2.Monitors 140 and 142 communicate with processor 150 and/or each othervia a wireless or wired network 160 to track and determining location oftags in one AREA 1 while simultaneously tracking information in AREA 2.

Tag 130 may be any device or combination of devices operative to receivea transmission from at least one locator and to broadcast its ownmessage, including received location information (e.g., Locator ID) tomonitor 140. In an optional embodiment, tag 130 includes a signalstrength analyzer circuit for distinguishing the signal strengthsreceived from the transmissions of respective locators 110 or 120. Bydistinguishing the received signal strengths, tag 130, or monitor 140and its associated processor, may distinguish between locator broadcastzones 111, 121. For example, if tag 130 determines that the strongesttransmission is associated with locator #2, tag 130 may broadcast onlythe Locator ID for locator #2 even though tag 130 also received a weakersignal from locator #1. By distinguishing the locator with the strongesttransmit signal it may be deduced that tag 130 falls closer to withinthe boundaries of a particular locator broadcast zone. In an alternativeembodiment, the Locator IDs of both Locators 110 and 120 may bebroadcast by tag 130. In this case, preferably the Locator IDs would bearranged in a hierarchical manner according to signal strength toindicate that tag 130 is closer to one locator than the other (e.g.,locator 120 ID and followed by locator 110 ID).

Monitor 140 may be any device or combination of devices for receivinglocation identification broadcast by tag 130. For example, monitor 140may be an RF receiver receiving wireless transmissions from tag 130and/or locators 110, 120. Moreover, monitor 140 may also include, or beconnected to, a respective processing unit 150 for determining locationsbased on the received location information.

The use of relatively inexpensive transmitting devices as locators 110and 120, assists to reduce the number of more complicated and expensivemonitors 140 required for a location identifying monitoring system.However, the present invention is not limited to unidirectionaltransmissions and receptions and may also, for example, utilize locatorsthat transmit to tags and receive from tags as well. Using this approachwith the SSI (signal strength indicator) circuitry, tag 130 may respondonly to the specific locator that lies nearest (i.e., locator 120). Withbidirectional communications the locators may communicate information tomonitor 140 or directly to a processing device (e.g., if the locatorswere networked to a computer system).

A further modification of system 100 is to include multiple antennas onthe locators or tags that serve to triangulate a position of the tags.For example, a tag can have two input antennas each at ninety degrees,or some other predefined angle to each other, to assist in calculatingthe direction of reception and from the locators. Alternatively and/orin addition, locators 110, 120 may include multiple antennas fortriangulating position to a more accurate degree.

As discussed in respect to FIG. 1B, system 100B includes a plurality offixed locators which operate determine a detailed fine location of thetag. This is a greatly enhanced feature in warehousing and otherapplications where not only the presence of an item can be determined,but also its fine location can be determined in a low-cost system withonly a limited number of monitors. If a series of locators arepositioned in a line or in a two directional pattern, then the detailedlocation of the tag can be readily determined. The equations thatdetermine position for a distance equal to half of the distance ofalternative pointers match up at the transition points. For example, ifpointers A, B, C and D are each located ten feet apart and the tag islocated under pointer B, then pointers A and C can determine the tagposition within the range of plus and ±2.5 feet from B with highlinearity. If the tag is moved to half way between pointer B and pointerC, the equation calculates the position using data from B and D. Thisprocess can be repeated in a long line or in an area or volume with bothx, y and z positioning. Any combination of the foregoing alternatives ormodifications may also be pursued and is to be considered within thescope of the present invention.

The present invention is superior to the high frequency operationrequired in ranging or time-measurement systems of the prior artsystems. High frequency operation can cause problems for certainoperating environments, for example, operation in a building with anabundance of signal absorbing and reflecting equipment and materials. Incontrast, the locator transmissions used in the present invention canoperate using a frequency on the order of 125 Khz range. Since signalattenuation decreases with frequency, the lower transmit frequencieseasily penetrate items and personnel. In the present invention, asopposed to many conventional systems, the output frequency of tag 130 isnot necessarily used to determine location of the tag, e.g., using timeof receipt, triangulation or phase angle determinations. If the tagtransmits in the typical three to nine hundred MHz range, a great dealof transmit overlap can be provided to insure reception by monitor 140.

Turning to FIG. 2, utilitarian aspects of a monitoring system will nowbe described. In example system 200, one or more container units 210,211 each include respective tags 212, 214. Locators 110 and 120 areplaced at strategic positions in and around a facility or area. Locators110 and 120 inform loading device 230 (e.g. an automated forklift,robotic loader or part carrier) where the tags 212, 214 (and associatedcontainers 210, 211) are within a few feet. If loading device 230includes its own tag 232, the position of loading device 230 may also betracked and/or determined using locators 110, 120. As previouslydiscussed, locators 110, 120 broadcast low frequency locationidentification information (e.g., Locator ID's or geographicalcoordinates). Tags 212, 214, and 232 may receive the locator broadcastand in response to receiving the locator broadcast, begin broadcastingtheir own message which includes the location identificationinformation, in the same format or another. A reader or receiving devicesuch as monitor 250 may receive broadcasts emitted from tags 212, 214and 232 and use the location identification formation to determine alocation of one or more containers 210, 211 and/or loading device 230.

Monitor 250 represents a receiver and/or an associated computer systemfor receiving, tracking and storing location identification informationbroadcast from tags 212, 214, and 232. Monitor 250 may be locatedcentrally or on the loading device itself.

In a basic system, the location of loading device 230 can be identifiedwithin a few feet. By analyzing signal strength strengths of tag and/orlocator broadcasts, the accuracy of location monitoring can beincreased. Furthermore, signals received from multiple locators can betolerated and distinguished.

The locator and/or tags can include multiple antennas that serve totriangulate position received broadcasts. If, for example, tag 232 onloading device 230 includes one antenna directed to the left and oneantenna directed to the right, the position of tag 232 (and henceloading device 230) can be readily determined in respect to knownpositions of locators 110, 120. One way of determining this position isto subtract the signal received from locator 110 from the signalreceived from locator 120. If loading device tag 232 is preciselylocated half way between locators 110 and 120, the output would be zero.If loading device moves in one direction closer to one locator than theother, the output provides one value and if the same distance is movedin the opposite direction the value would be the same only with areversed sign. If this difference is divided by the absolute sum of thetwo locator signals or another locator signal located between the two,then a radiometric relationship may be derived and maintained. Manydifferent antenna angles and methods can be utilized to obtain the samedetailed position resolving information. The actual calculations can beperformed in the tag or the information broadcast to a receiver andsystem for processing (e.g., monitor 250) or a combination of methodscan be employed.

Referring to FIG. 3, a location monitoring tag 300 according to oneaspect of the invention preferably includes controller 310, transmitter320, and receiver unit 330, and an optional power supply or cell 360.Receiver unit may include signal strength analyzer 340, message analyzer350 and a detector/decoder.

Tag 300 functions to receive signals having location identificationinformation through receiver 330, optionally, analyze strengths ofreceived signals if more than one signal is received, and broadcastsignals including received location identification information, such asa Locator ID or navigational coordinates or the like. Tag 300 mayfurther transmit its own identification information, control data andstatus information as well as any information received from otherdevices such as Locator IDs or other location information received froma locator unit. Such information can serve to determine the location oftag 300 since a locator unit is in a fixed defined location or locatedon a vehicle equipped with a global positioning system (GPS) receiver(see below). Tag 300 may also send battery status, input data and otherinformation in one transmission word or a series as required.

Transmitter 320 may be any device or combination of devices fortransmitting a signal. In an optional embodiment, transmitter 320 hasdual output stages that operate together, for example, with one havingzero degrees carrier phase and the other having ninety degrees carrierphase, or alternatively, the two outputs can be sequentially operatedwithout regards to phase. The two outputs may function to drive multipledirectional antennas for optimum performance at all angles when tag 300is located on metal objects.

Transmitter 320 may have the capability to operate in different modessuch as slow beacon only output, or a fast interrogated output, asdiscussed in more detail below. Transmitter 320 may output a single wordor up to eight words in a continuous transmission or independently witheach having sixteen bits of data to enable tag 300 to handle billions ofID codes.

In an example embodiment, transmitter 320 has the following features:

-   -   Output frequency of 433 MHz;    -   Output power level of 30 MW DC Maximum (Output stage) (set to        correspond to 100 uV Meters Quasi Peak measured at 3 Meters        (USA) or 500 uV Peak at 3 Meters (Japan);    -   Interrogated output rate of 0.25, 1.0, 10 (default) and 100;    -   Beacon only output rate of 1.0, 10 (default) and 100;    -   Dual state output, e.g., zero degrees (e.g., planar antenna on        card, and ninety degrees (e.g., vertical or external antenna);        -   Data output        -   Format: Type 1 for Beacon Mode; and Type 2 for Interrogated            Mode;        -   Modulation: amplitude ONOFF, Pulse Width;        -   Data Type: NRO (minimized DC Slew) Modified Manchester;        -   Clocking Type: self-clocking (RSCK);        -   Clocking Rate: 19.2 KBPS Nominal;        -   Transmission Rates: Max 0.25 second, next 1 second; next 10            second (default); Min. 100 seconds (programmable by locator            or setup unit);    -   Data Format:        -   Type 1—UMS (Universal Monitoring System) Programmed Time            Periods (Beacon or Non-Synchronous Interrogation Mode) with            encoding key;        -   Type 2—UMS Hierarchical (interrogated mode) with encoding            key (optional alternative or both);        -   Dibit Encoding—Dibit (2 quaduature encoded bits where 2^(nd)            bit is complement of 1^(st) bit) where Data Bit 0=00, Data            Bit 1=11, Control Start/Reset Bit=10, Control Stop/EOW (end            of word) bit=01;        -   Data and Control Bit Recovery Key: must match encoding, both            data and control outputs data and control outputs data and            controls must be complement to be valid, controls must lead            or follow data, controls and data must pass collision tests            defined below.

-   Word Format:    -   Word Length—24 dibits    -   Word Codes—64,000 (extra codes are reserved for control or        special purposes)    -   Word Format—Start=1 (Dibit) (01 Code))        -   Fixed=2 (01 Dibits) (10 Code)        -   Word#=3 (Dibits) (10 or 11 Code)        -   ID/Data=16 Dibits (10 or 11 Code)        -   Parity=1 Dibit (10 or 11 Code)        -   Stop=1 Dibit (01 Code)    -   Word Transmission Period—2.5 Msec. (limited by receiver chip)    -   Dual Word Transmission Period—5.42 Msec.    -   Eight Word Transmission Period—21.68 Msec.

-   Message:    -   # of Words—1-8 (words can be sent one at a time or contiguous        with added four stop dibits between words);    -   # of Codes—64,000 to the 7^(th) or 8^(th);    -   Message Check Word—Last word sent in a continuous message can be        a message check code if desired (optional).

Receiver unit 330 may be any device or combination of devices forreceiving and/or decoding a signal from a tag (e.g., tag 130; FIG. 1A).Receiver 330 is preferably capable of receiving a carrier signal in therange of 100 KHz to 13.56 MHz (depending on optional chip selection)from a setup unit or a locator unit. The locator unit(s) can operateindependently or synchronously under the control of a centralizedcontrol unit. Receiver 330 preferably receives a wakeup or start signalof eight bits or more followed by a twenty-four bit word individually orin groups of up to eight words. Receiver 330 optionally operate insampling mode where receiver 330 turns on and off intermittently. Forexample, it turns on for 100 usecs every 80 msecs (i.e., 800 to 1). Thiscorresponds to a broadcast from a locator unit having a start pulselength of 100 usecs and a repetition rate of 250 msecs or less. Samplingin this manner enables receiver 330 to minimize power drain and hence,maximize battery life. Functions of receiver 330 and transmitter 320 maybe combined into a single transceiver unit or they may be separatediscreet units. Antenna 322 may be a single shared antenna or multipleantennas.

Controller 310 may be any device for controlling transmit and receivefunctions of tag 300. Controller 310 may also be used for controllingsignal strength analyzer 340 or other optional and/or non-illustratedcomponents present on tag 300. In a preferred embodiment controller 310is a programmable micro-controller including a RAM for enabling writecapability.

If present on tag 300, signal strength analyzer 340 enables detection ofthe strength of signals received by tag receiver 330. By measuringsignal strength, distinguishing between received signal strength, or atleast decoding signals having a minimum threshold signal strength,handling of multiple received signals is improved and determination ofthe location of tag 300 may performed with improved accuracy.

Turning to FIG. 4, a simplified signal strength analyzer 340 functionsto identify differences in received signal strengths and/or select asignal with desired magnitudes. Signal strength analyzer 340 may alsoserve to rate a plurality of received signals according to theirmagnitude. In one embodiment, analyzer 340 is a digitally settable pulsethreshold circuit including a series of analog switches or digitalcomparators 410, 420 and 430. Comparators 410, 420 and 430 each receivea magnitude of a received signal in one of their two inputs. Analyzer340 also preferably includes a reference voltage source 440 forproviding varied reference levels to the second inputs of comparators410, 420 and 430. The magnitude of received signals may be identifiedand/or measured based on predetermined voltage references provided byreference source 440. Controller 310 (FIG. 3) uses information fromanalyzer 340 to control transmission of information, e.g., only theLocator ID associated with the strongest received signal. Alternatively,controller 310 uses information from analyzer 340 to associate receivedsignal strengths with the received locator IDs. The signal strengths ofeach received signal may be broadcast in the tag message. A monitor andassociated processor may use such information subsequent processing. Anyother type of device or combination of devices may also be used toperform the signal strength analyzing features discussed above.

Location Identification using a Navigational Receiver

Turning to FIG. 5, another type of location monitoring system 500 of thepresent invention includes vehicle 505, locator unit or other type oftransmitter 510, navigational information receiver 520, one or more tags530, monitor 540 and processing device 550. The purpose of system 500 isto determine, identify and/or articles 580 such as inventory, and theirlocation. System 500 utilized geographical coordinates or othernavigational information to serve this purpose.

In this embodiment, locator unit 510 and navigational receiver 520 areaffiliated with a position of, or attached to, vehicle 505. Locator unit510 broadcasts location identification information 511 while vehicle 505is in motion. The location identification information 511 preferablyincludes the current geographical position of vehicle 505 as determinedby navigational receiver 520. As vehicle 505 moves past inventory 580,inventory tag 530 receives the location identification informationbroadcast 511 and responds by tag 530 broadcasting its own information531 which preferably includes a Tag ID and the location identificationinformation from navigational receiver 520. Area monitor 540 may thenreceive broadcast 531 and associate the Tag ID with inventory 580 and ageographical position.

Locator broadcast 511 activates each tag in local vicinity so thattagged items can be located and inventoried. System 500 can identify arough location of each tagged item based on the navigational coordinatesbroadcast by the locator unit 510. This location identificationinformation may be transmitted to the tags and relayed by the tags tomonitor 540 for processing by processor 550. Alternatively, monitor 540and/or processor 550 may be located on vehicle 505 and associategeographical coordinates based on the position of vehicle 505 when abroadcast from tag 530 is received. For increased accuracy, locator 510should transmit extremely directional broadcasts.

In a modified aspect of the invention, system 500 does not require thatgeographical coordinates be transmitted to, and relayed by, the tags ifthe monitor or other reader device can discern the position of thevehicle using some other spacial relationship to the receipt of tagbroadcasts. Such relationship might be derived by, for example,connecting monitor 540 to navigational receiver 520 or navigationalcoordinates may be broadcast to monitor 540 from a transmitter otherthan tag 530, such as locator 510. In a further aspect of the invention,a signal strength analyzer may be utilized by monitor 540 or tag 530 tofurther increase the accuracy of determining the location of a taggeditem as discussed previously.

Mode Changing Monitoring Systems

According to various other aspects of the present invention, type oftags may also alternatively be able to send detailed locationidentification information in operation and under the instructions of alocal locator or low frequency transmitter (LFT) as discussed above.

In conventional systems the functions tags and their mode oftransmission (e.g., Type I and Type II) are largely predefined and notflexible in their use and thus may require that a merchant or supplierto carry more than one type of tag in an inventory depending on thedesired functionality. The present invention includes tags that arecapable of changing broadcast formats or finction. The formats and/orfunction of the tags in the present invention can be changedautomatically or initiated by, for example, a received transmissioncommanding the tag to change.

According to a first aspect of the invention, a tag that is idle (e.g.,not moving) for a predetermined period of time may send a beacon inasynchronous format with time diversity to minimize collisions betweenreceived tag transmissions. However, when receiving certaintransmissions from other devices, (e.g., interrogation from a locator orother device) the tag according to one aspect of the invention may beginto transmit in a synchronous format. The synchronous format allows alltags that are activated by the locator or other device, to transmit witha minimum of tag collisions. This type of switching enables fastertransmit operation when needed, (e.g., instantaneous identification orlocation requests) as well as slower asynchronous operation at othertimes. The mode of tag operation can be selected as required to meet aparticular situation at a particular time.

Turning to FIG. 6, a method 600 for switching modes or formats in awireless monitoring system includes generally, a tag broadcasting in afirst transmit mode 610, a first event occurring 620, the tagtransmitting in a second transmit mode 630 in response to the occurrenceof the first event, and continuing to transmit in the second transmitmode unit the occurrence of a second event 640, the second eventinitiating the tag to return transmitting in the first transmit mode620.

The first and second events can be selected for any type of event whereit is desired to track the occurrence or non-occurrence of that event asdiscussed above where beacon mode is transmitted until a locatortransmission is received (first event) when the tag begins transmittingin a second synchronous mode. In this case, the second event may be theexpiration of a timer in the tag or a halt in receiving the transmissionfrom the locator unit.

In a tag motion detection embodiment of the present invention, when themotion tag is idle for a certain period of time, the tag may send beaconasynchronous transmission (with time diversity) to minimize collisions.However, when motion tag starts in motion (e.g., first event), the tagwill begin transmitting in a second transmit mode, for example, asynchronous transmission. In one aspect of the invention, the secondtransmission mode is exactly the same (e.g., same period and pulses) asthe first transmit mode with the exception that when the tag detectsmovement, the beacon transmission resets and begins again. Such a resetduring a previously uninterrupted pattern of beacon transmissions can beused by a monitor/detection processor to discern when particular tagsare in motion. When the motion tag stops motion, or a timer expires,(e.g., second event), the tag returns to its first transmit mode.

Changing between the first and second transmission modes may includechanging the content of the transmission as well as, or instead of,changing the format of transmission. In one aspect of the invention, thetype of information transmitted from the tag can be varied automaticallyor by command. For instance, a beacon tag may be normally configured totransmit certain information such as its Tag ID, time of day, lastmovement, etc. as part of its message. However, according to one aspectof the invention, a locator or other transmit device may sendinstructions to the tag to change the content of the message beingtransmitted. Such change in content may be, for example, to include abattery level status or other type of content desired. In this case, thetag would begin to transmit the battery level in place of, or inaddition to the last movement information. The substitution or additionof information may vary depending on the format utilized fortransmitting (i.e., how much payload may be present in the tag message).

In another aspect of the invention, the periods, gaps, start pulse, endof word and other relevant message formatting information may be variedby a command from a transmitting device, e.g., locator or reader. Theflexibility associated with being able to configure the format andcontent of tag transmissions using established transmitting units e.g.,locators, provides significant advantages over the wireless monitoringsystems of the prior art. By way of example, tags for certain types ofinventory may be assigned a particular type of transmission format orcontent while tags for other types of inventory or new inventory beassigned a different transmission format or content, where such controland assignment is based solely on centralized software control andexisting transmitters or locators rather than complicated setup units.

Referring to FIG. 7, one or more tags 730 may be, for example, mountedon a mobile package carrier 710 and transmitting its identificationand/or other information at a slow beacon rate. During the slow beaconrate mode the presence and general location of tags 730 can be trackedwithin distances of, for example, a hundred feet. When mobile packagecarrier 710 moves through a door or other access point, tags 730, 732come into close proximity of a locator unit (e.g., locators 110 or 120).When in close proximity, tags 730, 732 encounter a broadcast fromlocators 110 and/or 120. In response, tags 730, 732 begin to transmitinformation at a higher rate; such information including, for example,Tag ID as well as other information such as locator ID from locator 120.

In one aspect of the invention, locator units 110, 120 can instruct tags730, 732 to switch into a different type of mode, for example, turn off,turn on, operate at low, medium or high rates, operate for a period oftime and then turn off, change the type or formation of information tags730 transmit, or in other desired modes. Using this type of selectedoperation, tag battery power may be conserved as the tag can beinstructed to transmit only when necessary or desired. By way ofexample, a number of tagged packages 750 located on carts 770, 772 beingpulled by a vehicle 710 through an area having locators 110, 120, canindicate their identification, where they are and their order behind thevehicle. Locator units 110 or 120 can turn off the tags when, forexample, the package carriers are put on to an airplane and, conversely,they can be turned on when removed.

Each tag preferably comprises a transmitter, receiver,micro-controller/interface and an optional battery. A summary of theinventive hardware aspects include one or more of the following:

-   -   Dual antenna outputs for diversity transmission;    -   Extended battery life under pointer control;    -   Local position input from pointer;    -   Beacon and/or Interrogated Operation or Both;    -   Encoded Bits for collision management;    -   Dual anti-collision modes of operation including asynchronous        and synchronous;    -   External Programming on Board (external I/O);    -   Write data and control capability;    -   External reset input;    -   Watchdog timer for automatic restart;    -   Optional on board cell battery; and    -   Sampling receiver for reduced power consumption.        The inventive tags, in conjunction with a pointer unit can be        used to provide the following optional or programmable        functional aspects:    -   Turn on transmission when in range of the pointer;    -   Turn on when in range of the pointer for a present mode and time        when out of range;    -   Turn on until turned off;    -   Turn off until turned on;    -   Turn off tag while in proximity and on when out;    -   Select the tag mode and transmission rate;    -   Send pointer unit address, data, control, and status information        for instruction and retransmission in the same or alternative        form; and    -   Synchronize tag for operation in Type 1 format to minimize        collision, speed up the read rate and provide time and data        information.

Preferably, the tag transmitter has optional dual output stages thatoperate together with one having zero degrees carrier phase and theother having ninety degrees. Alternatively, the two outputs can besequentially operated without regard to phase. The transmitter canoperate in different modes such as a slow beacon only output or a fastinterrogated output.

Monitoring System Communication Protocols

The Type 1 and Type II formats employ encoding and pulse positioning forcommunication in synchronous and non-synchronous environments. Asignificant aspect of these protocols is the concept of using theposition of a pulse in a transmission as a means of coding the Tag ID orother information. Another important concept of the present invention isthe transmission of complementary information to improve communicationintegrity. In addition, a pulse can be a single entity or it can befurther broken down into sub pulses or encoded.

Turning to FIG. 8, an example protocol used in wireless monitoringsystems will now be described. The primary purpose of the followingprotocol is to enable a receiving unit and/or associated processing unitto decipher or read multiple transmissions when two or more tags happento begin transmitting at the same time. The following heading describethe situations where two tags randomly begin transmittingsimultaneously:

-   -   XMT-1 and XMT-2—represent a word transmitted from respective        tags;    -   RCVD—represents the transmitted and/or noise signals received by        the system receiver;    -   WORD—represents an example period and parts of a single word        transmission of the inventive protocol;    -   Word Slot #—represents the number of slots in the period of a        single word;    -   Part Slot #—represents the slot number of the respective parts        contained in the word; and    -   Time—represents segments of time through the signals beginning        with the first edge of a start pulse and ending with the stop        gap of the word.

There are three primary rules of the inventive protocols which will bediscussed first in respect to their purpose.

Protocol Rule #1:

A valid tag transmission must include two parts, a first part and asecond complementary part. Pulses in PART-A must appear in complement inPART-B. (PART-B pulses are inverse in magnitude and time with respectpulses in PART-A).

Protocol Rule #2:

A valid tag transmission must include a predetermined number of pulsesand a minimum gap between the pulses. In the exemplary embodimentdepicted in FIG. 8, a valid protocol must include two pulses in PART-Awhich are separated by four or more slots.

Protocol Rule #3:

Each tag transmission must include a specific start, stop and gapconfiguration. In the illustrated example, each transmission includes: astart pulse having a width of four slots; a first gap consisting of fourslots immediately following the start pulse; a second gap consisting offour slots between PART-A and PART-B; a stop pulse having a width offour slots; and a third gap consisting of four slots immediatelyfollowing the stop pulse.

As shown, the timing sequence for the first word is as follows: T1=beginstart signal; T5=end start signal, begin gap 1; T9-end gap 1, beginPART-A; T38=end PART-A, begin gap 2; T42=end gap 2, begin PART-B;T70=end PART-B, begin gap 3; T75=end gap 3, begin Stop signal; and T77end stop signal. A second word may begin at T77 (e.g., rising edge ofstart signal as at T1 may occur at T77) or any time thereafter.

Individual pulse representations in slots represent assertions in thatslot. An assertion may be a high or low signal representing a receivedsignal including noise. Each assertion may be communicated by a codedsignal having more than one “pulse” such as when a binary number code ofseveral bits indicates assertion (e.g., 1011=yes; 0101=not asserted).Modulation of the signals may be any conventional type including FSK,PSK, FM and AM

RCVD Signal:

Based on the four pulses in PART-A of the RCVD signal, up to six tag IDcombinations could be present the depicted configuration with only twotag transmissions are present (two pulses for each transmission). Usingthe foregoing Protocol Rules, the actual Tag IDs are readily determined.The following table represents the analysis of received signals andresulting logic conclusions: Possible Pulse Pairs (as identified by PartSlot #) Conclusion Rationale 1, 6  Valid, present Min. Spacing OK, bothcomplementary parts present. 1, 9  Valid, present Min. Spacing OK, bothcomplementary parts present. 1, 12 Invalid, ignored PART-B pulse missingat 12 6, 9  Invalid, ignored Not four slots between pulses 6, 12Invalid, ignored PART-B pulse missing at 12 9, 12 Invalid, ignored Notfour slots between pulses; and PART-B pulse missing at 12

As seen from the known transmission signals, XMT-1 is a tag transmissionwith 1,6 ID and XMT-2 is a tag transmission with 1,9 ID.

A start pulse(s) is used to define the beginning of a messagetransmission. The start pulse can be a continuous carrier for a definedperiod of time (example above, four periods) or it can be a square wave,a series of 1's and 0's or a specific code or otherwise unique indicatorof the start of a transmission. Utilizing a pulse which follows acertain length of gap or blank period cant further define it as a uniquestart function. The start pulse is then uniquely different to thefollowing data or other stop or control pulses or information and,therefore, can be readily determined and identified with respect to theportions of the message or other messages. In the example of FIG. 8, thestart of the message is indicated by the four period start pulsefollowed by a gap of four time periods. Other protocol parameters may beused and the specific length of time may vary.

A unique stop pulse is also used to define the end of a message wordand/or the end of a message. The stop pulse is similar to the startpulse in that it is uniquely different from the start pulse, message,data and control information. In the depicted embodiment, a stop pulsewidth of two periods is used.

The first message word is constrained between the initial start pulseand the first stop pulse. Following words are contained between the stoppulses of one word and the next. In other words, a group of back-to-backwords may have only one start pulse for an entire group of words. Inthis case, an additional stop pulse can follow the last word of amessage, e.g., end of word (EOW) and end of message (EOM) indication. Inthis embodiment, the EOM is followed by a blank time, e.g., eightperiods. A much greater blank time may be used between transmissions ofanother message by the same tag. In a common environment the messagetransmission might take ten milliseconds and the next transmission mightnot occur for ten seconds or more. In addition, the following period mayvary from message transmission to message transmission as part of aprogrammed time diversity to minimize the chance that tag transmissionswill collide.

As discussed above, four pulses are used to transmit the identificationor ID of the tag or other control, sensor, status, data or otherinformation; two pulses in PART-A and two complementary (complementarywith respect to level and time) pulses in PART-B. In a typical message,ID or data is transmitted in seventy time periods (76 total minus fourstart pulse and two stop pulse time periods) between a start pulse and astop pulse or between two stop pulses.

In the dual pulse example of FIG. 8, the first assertion of data (a zerovalue) is when the first pulse is located at word slot position nine(PART-A slot no. one) out of seventy-six periods and the correspondingcomplementary pulse is located at word slot position 70 (PART-B slot no.one) out of seventy-six. All valid pulses have a minimum of four spacesbefore and after them. These periods can be considered “anti-pulse” thatare part of differentially confirming the presence of the pulses. Thesecond assertion of data is represented by a pulse at word slot positionfourteen (PART-A slot no. six) with its complementary pulse at Word slotposition sixty-five (PART-B slot no. six). However, a minimum spacing ofanti-pulses must be maintained between the first, second and fourth bitsin the message. Therefore, as the first bit moves to a higher slotposition in PART-A, the other alternatives for bit pulses is reduced.For example, if twenty-nine part slot numbers are available with arequirement of a four period gap between PART-A and PART-B, a total ofthree hundred mutually exclusive alternatives are possible. Generally,two hundred and fifty six of the three hundred may be used for ID ordata coded for zero to two-hundred fifty six (i.e., 256 alternatives)and forty-four remaining alternatives are used to identify specialcontrol information.

In a typical message the first word is a control word that defines theremainder of the message. The following ID words are typically a seriesof three words can then define 256ˆ3 alternatives or sixteen millionalternatives. Four words can define four billion codes. One advantage ofthis protocol is that the processing of the information for one messagecan be performed without any previous knowledge of what code isexpected. A full reading, assuming no collisions that might cause amessage to be corrupted, can occur on a word or message basis. Noinformation needs to be stored from one message to another. In essence,each message received, even if it overlaps other messages, can betreated as a single message for interpretation and decoding purposes.For example, if message A is received as initiated by its start pulse,and message B is received while A is still in the process then thereceiver system only needs to read message A as one event and message Bas another. Using high speed processing such as that employed inhigh-speed DSP, each event can time-share the processing task.

Another received overlapping message C can have a timer assigned and itsmessage decoded or deciphered individually in a multiple task-processingenvironment. The messages might interfere with each other occasionally,however, this will result in individual message errors with eachmessage. The cause and reason for the error does not necessarily have tobe determined and each message can simply be treated as an independentevent. In higher level of decoding it is possible to review all messagesreceived and determine how one message might have introduced an error inanother. It then perhaps is possible to correct for the error since thereasons are known.

It has been calculated that a message rate and density or number of tagsthat should cause overlapping and potential collision of about fortypercent will provide a maximum throughput rate. This assumes thatmessages that are tightly compressed with minimum periods possible mighthandle overlaps of three to five messages with a nominal being three.This is a function of the density of the message. The messages can begreatly lengthened in order to minimize overlapping collisions. However,this can create its own problems since it is desired to have theshortest message length possible to provide the maximum time for eachmessage to be communicated without overlaps or collision.

A significant advantage of the inventive protocols is that pulses needonly to be determined to exist in one time period or another. A complexreading of encoded bits is not needed. A differential comparison can bemade between a derived base reference level in the decoder and the leveland status before and after every pulse pattern; that is, theanti-pulses can be compared in an analog and/or digital fashion to thepulses. Every data or ID pulse by definition should have four emptyspaces or anti-pulses before and after except in the case where theremight be an overlap between two or more tags. In this case one or moreof the spaces between pulses should be off or zero or be an anti-pulse.If the anti-pulses have an amplitude of, for example, one volt and thepulse presence results in four volts then a differential read betweenthem is three volts.

The previously described protocol can be used in a synchronous and/ornon-synchronous environment. Tags can be synchronized when they areactivated by the same event such as movement or receive a signal thatcauses them to initiate transmission. In a non-synchronous environmentall the tags are randomly timed and have no set relationship betweenthem. In a synchronous environment the tags are all timed to starttogether at the same time and, therefore, have a greater chance tocollide.

Alternative Protocol Features

According to one aspect of the invention, assertions may presented usingamplitude keying, e.g., assertion=the carrier signal on, andnon-assertions=the carrier signal off.

In another protocol variation, in a word transmission from a tag to areceiver, from a transmitter to a tag, or from a transmitter to areceiver (e.g., locator to receiver), the first word of a transmissionmay have a fixed format which includes control codes defining the formatto be used for the second and following words. The second and followingwords (until another control code is received for changing word formats)may include more or fewer time slots per PART. A differentassertion/non-assertion technique may be identified by a suitablecontrol code.

In yet another variation of the monitoring system protocols, PART-A (andinversely PART-B) may be divided into discreet portions of consecutiveslots referred to herein as “subparts.” Turning to FIG. 9, WORD 900format is similar to that discussed in respect to FIG. 8 but is dividedinto subparts. By partitioning the slots in the format of word 900,multiple pieces of information content such as sensor or batteryreadings, memory or register contents, can be conveyed independent ofother subpart contents.

According to yet another variation of the monitoring system protocols,the signal strength of a transmitted assertion may be used forattributing assertions to a specific transmitting source (e.g., tag orlocator). In this variation, the magnitude of a transmitted signalrepresenting assertions from stationary transmit sources will varyaccording to the transmit source distance from the receiver or obstaclesin there between. By tracking magnitude of these signals, the varioustransmitting signals can be distinguished, particularly when assertionsoverlap one another.

In another variation of the monitoring system protocols, transmittedsignals may be selected (or rejected) based on a threshold signalstrength. A multiple threshold comparator circuit (such as that shown inFIG. 4) and/or digital filtering techniques may be used to accomplishthis end. By using a multiple threshold detector, the sensitivity of thereceiver may be set to different levels for different purposes. Forexample, a higher threshold level can be used to read the closer andshorter pulse length tag signal and a lower level can be used to capturelong range, but longer period and pulse length transmissions. As withthe comparator discussed in respect to the tag signal strengthcapabilities discussed previously, the resulting detected signals can be“and'ed” or “or'ed” together so that a strong signal overrides a weaknoisy signal but a weak, noisy signal can still be read.

Alternatively, signals may be selected or rejected based on frequencyranges (one or more bandpass filters may accommodate this type offrequency monitoring).

The present invention has heretofore been discussed primarily in respectto broadcasting transmissions in the context of radio wave and/ormicrowave transmissions. Notwithstanding, the present inventionincluding monitoring systems and related protocols may be used in anytype of wireless communication utilizing any frequency ofelectromagnetic waves. Specifically, it is contemplated that broadcastsbetween system components may be performed using infrared or othercommunication techniques in the visible and non-visible light spectrum.

Unless contrary to physical possibility, the inventor envisions themethods and systems described herein: (i) may be performed in anysequence and/or combination; and (ii) the components of respectiveembodiments combined in any manner.

Although there have been described preferred embodiments of this novelinvention, many variations and modifications are possible and theembodiments described herein are not limited by the specific disclosureabove, but rather should be limited only by the scope of the appendedclaims.

1. In a system for monitoring location of tags, a method performed by atag for transmitting a tag message, the method comprising: determingwhether the tag has been moved since an immediately prior tag messagetransmission; and if it is determined that the tag has been moved, thenbeginning transmitting the tag message without awaiting lapse of anintermessage gap; otherwise, beginning transmitting the tag messageafter lapse of the intermessage gap.